Optically controlled actuators have been used as an alternative to electrically control actuators in critical control systems. Control systems containing optically controlled actuators offer a number of advantages for aircraft, industrial and military applications with respect to conventional electrical actuators. These offer a reduced explosion hazard, increased electrical noise immunity and weight savings. They offer better survivability in the presence of electromagnetic interference, electrostatic interference, electromagnetic pulse and high energy particle radiation.
Optically controlled actuators can be either indirectly controlled or directly controlled. An indirectly optically controlled actuator uses an optical communication link to control a conventional actuator but the optical signal is converted to an electrical signal for activation of the actuator. Directly optically controlled actuator uses an optical communication link to directly control the actuator without converting the optical signal to an electrical signal. This is accomplished by the known use of an opto-mechanical interface to convert the optical signal to some mechanical signal such as a differential pressure signal. Such apparatus is known from U.S. Pat. Nos. 4,512,371, 4,606,375, 4,610,274, and 4,722,365. This actual pressure differential is then used to activate the actuator.
For most applications using either type of optically controlled actuator, a position feedback loop is needed in the control system to prevent degradation in system performance due to component and/or environmental changes. This also provides a tight control loop to rapidly move the actuator to the requested position without involving the time lag which would be required to feed the result of the actuated component change back through the remainder of the control system. In previous optically controlled actuator systems this has been accomplished by providing a conventional position transducer attached to the actuator with the output of this transducer fed back to the control system computer. Since the feedback signal be returned to the control computer, which is usually located some distance from the actuator, it is subject to the electrical interferences and other potentially degrading phenomena. This also requires computer time which may be at a premium in controlling an overall complex system.